GMW GMW8 PDF

This standard covers the requirements for hot dip coatings, both galvanized and galvannealed, applied to a sheet steel substrate utilizing a continuous hot dip process. The substrate may be cold or hot rolled sheet steel. Additional requirements or agreements shall be specified by regional GM Automotive Operations (GM) business units [e.g., North America (GMNA), Europe (GME), Latin America (GMLAAM), and Asia Pacific (GMAP)].

Material Description.

The type of coating and its mass and finish are specified by suffixes added to the basic specification number. The first two letters HD will designate a continuous hot dip coating. The coating mass for each side is designated by a minimum value in g/m². Only coating masses shown in Table 1 shall be used unless Materials Engineering is consulted. Other coating masses shall follow the same designation method. The letter G designates a pure zinc coating (galvanized) and the letter A designates a zinc-iron alloy (galvannealed) coating. The first set of digits along with the letter designation specifies the coating parameters of the unexposed side. The remaining designation specifies E (exposed), Z (semi-exposed), U (unexposed), or T (temperrolled).

Symbols.

Not applicable.

Typical Applications.

Sheet metal parts consisting of steel grades as described in GMW2M, GMW3032M or GMW3399M.

Remarks.

Not applicable.

Finish Suffixes.

Exposed (E).

A finish produced by eliminating all visual spangle pattern and surface defects per paragraph 3.1.3.3, to be used for critical appearance applications.

Semi-exposed (Z).

A spangle free finish produced by minimizing surface defects per paragraph 3.1.3.3 is used for secondary visible surfaces that do not require an exposed quality finish.

Unexposed (U).

A minimum spangle finish used for non-critical appearance applications. See paragraph 3.1.3.3.

Temper Rolled (T).

This surface shall have sufficient temper rolling such that luders lines or stretcher strain will not show when formed and painted. All other requirements are the same as U surface described above.